1. Field of the Invention
This invention relates to battery voltage checking apparatuses and methods, and particularly to battery voltage checking apparatuses and methods (or BC apparatuses and methods) for a camera using a battery as a power source.
2. Description of the Prior Art
In a known battery checking arrangement, two voltage levels are preset. One level is present to a value somewhat higher than a minimum voltage required for operating the device in which it is used, such as a camera, the other is set at a value close to the minimum operating voltage. The system provides a warning concerning the battery's energy consumption as a result of a determination made on the basis of the former level, i.e., the warning level. Erroneous camera action is prevented by inhibiting operation in response to a determination made on the basis of the latter level, i.e. the inhibiting level.
Cameras employing batteries generally use a silver battery of small capacity. Therefore, after a power source switch (hereinafter identified as switch SW1) is closed, the source voltage tends gradually to decrease. If a system determines the output voltage level of the battery when the source switch SW1 is closed, it cannot detect the battery's energy consumption state that ensues. To avoid this problem a conventional battery checking method does not make a determination based on the inhibiting level immediately after the switch SW1 is closed but accomplishes this by allowing a battery voltage checking load current momentarily to flow after a predetermined lapse of time from the closing of the source switch SW1, but only after closing of a shutter release switch (which may be called the switch SW2).
However, it is necessary to warn a user concerning the battery's energy consumption condition before carrying out an inhibiting action. Therefore, a determination based upon the warning level is made prior to and not after the closing of the switch SW2. For example, a battery voltage checking load current is allowed to flow when a switch which is specifically provided for checking the battery voltage is closed.
In conventional devices, two level determining actions are performed at different times as mentioned. However, such a conventional arrangement results in a complex battery checking circuit. Besides, the time difference between the two level-determining action makes it difficult to determine the output of the battery in the same condition. Thus, there is the possibility that the inhibiting action might be performed prior to a warning display, that is, the display of the result of the determination might be reversed. More specifically, while the battery voltage may be determined to be normal during the warning level test, at the time of the ensuing inhibiting level determination, the result may be the reverse of the warning level determination and may represent an inhibiting level which is lower than the warning level due, for example, to a temporary overload or the like. In such a case, the camera's operation has been inhibited prior to a warning display or annoucement to replace the battery. This is a serious problem in a system like a photographic camera which is required to inform the operator in advance of the need to replace a battery.